Algorithms

What are algorithms?

An algorithm is a sequence of instructions or a set of rules to get something done.

You’ll favour a particular route home from school – you can think of it as an algorithm. There are plenty of alternative routes home, and there’ll be an algorithm to describe each one of those too. There are even algorithms for deciding the shortest or fastest route, such as form the basis of satnav systems.

Algorithms are written for a human, rather than for a computer to understand. In this way, algorithms differ from programs.

A diagram showing the stages of making jam-on-toast.

A table showing how digits shift through place values when multiplied by ten.

A set of rules - an algorithm - for multiplying a number by ten.

Why are algorithms important?

Computer scientists strive for algorithms which solve problems in the most-effective and efficient ways – getting the most-accurate results, in the quickest time, with the fewest resources (memory or time).

Search engines such as Bing or Google use algorithms to order a list of search results so that, more often than not, the result we want is at the top of the front page of results. Your Facebook newsfeed is derived from your friends’ status updates and other activity, but it only shows that activity which the EdgeRank algorithm assesses to be of most interest to you. Your recommendations from Amazon, Netflix and eBay are algorithmically generated, based in part on what other people are interested in.

What do algorithms look like in the Primary curriculum?

Helping pupils get an idea of what an algorithm is needn’t be confined to computing lessons. A recipe in cookery, instructional writing in English, the method for a science experiment: each can be considered an algorithm.

For various activities, pupils will already follow a sequence of steps – e.g. getting ready for lunch or going to PE. In maths, one’s approach to mental arithmetic might be an implementation of a simple algorithm. Another example would be that of a teacher’s lesson plan.

A drawing of some flowers with four steps to planting a seed.

A sequence of instructions - an algorithm - for how to plant a seed.

A chart showing the different spellings of the "or" phoneme, and where they are used.

Spelling rules for the "or" phoneme.

3 - 5 years

Teachers naturally create opportunities for sequencing, which is a key element of algorithms. Children learn to take turns with others, to tidy up and line up. Sequencing happens during roleplay activities; for example, the events which occur when we go to post a letter at the Post Office.

5 - 7 years

There are many opportunities within the school day for children to understand algorithms and create their own.

The algorithms pupils create can often be implemented using programmable toys or "human robots", and it can be useful for pupils to compare how a square is drawn with a floor turtle and with Logo or ScratchJr.

As the children break down larger tasks into smaller instructions, they also develop their use of decomposition to solve a problem.

7 - 11 years

Increasingly, pupils apply algorithms as rules to their understanding of maths and grammar. They might create algorithms for how to multiply by 10, 100 and 1,000. They increase their understanding of algorithms as sequences of instructions – perhaps writing one for how to play their favourite sport – and they build their understanding of how algorithms and programs are distinct but intrinsically linked.

They gain confidence implementing their algorithms as programs using languages like Scratch. Whilst such graphical programming languages may make a planning stage seem unnecessary, writing down the underlying algorithm will make it much easier for pupils to discuss their algorithms and to get feedback from others before tackling the coding. To write the algorithm down, they might employ a storyboard or flowchart, simple rough jottings or “pseudocode” (a written description of how a program will operate).

Pupils are expected to think algorithmically, using decomposition confidently, to design programs with particular goals. They should be able to debug them. Errors and inconsistencies can quickly be discovered if pupils follow the instructions themselves, before writing these as code. In later years they’ll refine their algorithms further, demonstrate more-complex thinking and employ selection and repetition.

Find out more about algorithms / Downloads

Computing At School / Naace (2013): “Computing in the national curriculum – a guide for Primary teachers” (opens in a new window)

Phillip Bagge’s sandwich bot (opens in a new window)

Older pupils, or those needing to be challenged, can look at different types of algorithms, including sorting and searching algorithms, for example in this CS Unplugged searching-algorithm activity based on the game Battleships (opens in a new window)

… or this activity which teaches sorting algorithms with the Horrible Histories kings and queens song (opens in a new window)

Cormen, T. (MIT Press, 2013): “Algorithms unlocked”

Kevin Slavin talking about how algorithms shape our world

BBC Bitesize on algorithms (Key Stage 2) (opens in a new window)

BBC Bitesize on algorithms (Key Stage 3) (opens in a new window)

Activities that are great to get you started:

These activities develop pupils' understanding of algorithms.

Crazy Character Algorithms

Age:5-7 years
Concepts / Approaches: Logic, Decomposition, Debugging, Algorithms
Curriculum Links: Art, computing, English

Pupils will create a set of instructions on how to draw a crazy character and so start to understand what algorithms are.

The Crazy Character Algorithms has been rated 5 stars

Sharing Sweets Algorithms

Age:5-7 years (can also be adapted)
Concepts / Approaches: Patterns, Algorithms
Curriculum Links: Maths

A short, unplugged activity in which your pupils work out a simple set of instructions (algorithm) on how to share sweets, and adapt the instructions for differing amounts of friends. In so doing, they are using pattern to create a general rule for sharing.

The Sharing Sweets Algorithms has been rated 5 stars

Logical Number Sequences

Age:9-10 years (although can be adapted for other ages)
Concepts / Approaches: Persevering, Collaborating, Logic, Patterns, Algorithms
Curriculum Links: Maths

Pupils explain the rule for a number sequence and predict which numbers come next, extending their knowledge of simple rule-based algorithms and using logical reasoning.